In a multi service-provider wireless communication environment, such as a cellular network, multiple service providers may operate in a given geographic area, for example, a metropolitan area. Each service provider will have its own "geographic network" in that area, and will be assigned a unique operational "frequency" (which may comprise multiple frequencies, or a frequency band) for that geographic area. The service providers may have other geographic networks in other geographic areas. However, in those other geographic areas the service providers may be assigned different operational frequencies.
The invention relates to how a subscriber's cellular phone selects, and "registers onto", a particular range of operating frequencies (or "frequency band"), such as, for example, the frequency band assigned to the subscriber's selected service provider, in the geographic area in which the subscriber's cellular phone happens to be located and operating. (In this patent, the term "cellular phone" refers to a wireless, mobile phone that operates in a multi service-provider environment, usually a cellular environment. The term "registers onto" includes not only the processes involved in establishing a call, but also includes any communication between the network and wireless communication device, such as, for example, when the device is in standby mode. In particular, these "registrations" may give the network information, for example, on the location of the device.)
In early versions of cellular phones, the subscriber's phone would be pre-programmed so that on being turned on, i.e., "powered-up", the phone would operate at a pre-selected band, or would implement a pre-programmed search schedule to find a particular operating frequency band in accordance with the pre-programmed schedule. For example, the schedule might call for seeking service on a particular band and, if no service could be found on that band, the schedule might call for seeking service from non-preferred providers located on other bands. In later devices the pre-programmed schedule in the phone could be manually altered by the user.
However, it should be recognized that in these early implementations the number of possible bands were few and there were only a small set of hailing frequencies, sometimes called "control frequencies". Accordingly, in implementing a search schedule, all of the control channels could be scanned in a relative short period of time. However, as many more frequencies became available, many more control channels would have to be scanned to implement search schedules. This is a time consuming process, and consumers will not tolerate the associated delay on power up.
To address this intensified problem of searching rapidly for available appropriate frequencies, more efficient search protocols were devised to enable the subscriber's phone to search, efficiently and rapidly, through the various available operational frequencies for one assigned to the subscriber's service provider, or, in the absence of its service provider in the specific geographic area, for one assigned to a service provider with whom the subscriber's service provider had a "partnering" arrangement. (Such protocols usually have to be implemented whenever the phone is powered-up, even when in its home area, because the phone does not know that it is in its home area until it has found a channel that is broadcasting its home area identities. However, since the purpose of such search protocols is to enable more effective roaming operation, the protocols are called "roaming" schedules, even though they are most often implemented in the subscriber's home area, where the subscriber is not technically "roaming". It should be noted that with the ability to "roam"--i.e., operate outside one's home area, the "wireless network" is broadened to include all networks on which the subscriber may get service.)
This invention involves "intelligent roaming"--improved techniques for subscriber selection of an optimum service provider when the subscriber's phone is powered-up, whether in the subscriber's home area or while roaming. The invention is an improved technique for intelligent roaming and is best understood in the context of the frequency band allocation used in current wireless communications. FIG. 1 illustrates a portion of the radio frequency spectrum used today in such wireless communications. Frequency range 10, centered around 800 MHz, has historically been known as the cellular frequency range. Frequency range 12, centered about 1900 MHz, is a more recently established frequency range associated with personal communication services (PCS). Each range of frequencies, i.e., the cellular and PCS, are broken into two portions; an uplink portion, that is used for communications from a mobile communication device to a base station such as a cellular base station, and a downlink portion, that is used for communications from the base station to a mobile communication device. In cellular frequency range 10, the uplink portion is labeled 14, and the downlink portion is labeled 16. In the PCS frequency range, 12, the uplink portion is labeled 18 and the downlink portion is labeled 20.
Each of the frequency ranges is broken into bands which are typically associated with different service providers. For example, in the U.S., the FCC has allocated frequencies and frequency bands within its jurisdiction as described in the present application. But other nations, for example the UK or China, may have regulators that have determined a different frequency allocation for their cellular and PCS bands. In the case of cellular frequency range 10, frequency bands 30 and 32 are designated band "a" for uplink and downlink communications, respectively. In a particular geographic area, a cellular service provider is assigned frequency band "a" for use in mobile communications. Likewise, in the same geographic area another cellular service provider is assigned frequency bands 34 (uplink) and 36 (downlink) which are designated band "b". The frequency ranges assigned to the two service providers are sufficiently separated so as to not interfere with each other, thereby enabling the two separate service providers to offer service in the same geographic area.
Recently, the US Government auctioned the PCS frequency spectrum to service providers. As with the cellular frequency range, the PCS frequency range is broken into several bands with different service providers licensed to use different frequency bands within a particular geographical area. The PCS bands are referred to as A, B, C, D, E and F. The A band includes uplink band 50 and downlink band 52. The B band includes uplink band 54 and downlink band 56. Band C includes uplink band 58 and downlink band 60. Each uplink and downlink band of the A, B and C bands is approximately 30 MHz wide. The D band includes uplink band 62 and downlink band 64. The E band includes uplink band 66 and downlink band 68. Likewise, band F includes uplink band 70 and downlink band 72. The uplink and downlink bands of bands D, E and F are approximately 10 MHz wide each. It should be noted that in the combined cellular and PCS frequency bands, it is possible to have as many as eight different wireless communication service providers in a particular area.
Each of the different cellular and PCS bands consist of control channels and communication channels in both the uplink and downlink direction. In the case of analog cellular bands, there are 21 control channels for both the "a" and "b" bands. Each of the control channels include an uplink and a downlink portion. The control channels transmit information such as a SOC (System Operator Code), a SID (System Identifier Code), paging information, call setup information, and other overhead information, such as information relating to registering with the mobile communication system. The portion of the cellular band's spectrum not occupied by the control channels is used for communication channels. Communication channels carry, for example, voice or data communications. As noted above, each channel consists of an uplink and downlink communications link.
Presently there are several cellular communication standards. An analog standard known as EIA/TIA 553 was built upon the AMPS (Advanced Mobile Phone Service) standard. This standard supports 21 analog control channels (ACC) and several hundred analog voice or traffic channels (AVC). A newer standard is the EIA/TIA IS54B standard which supports dual mode operation. Dual mode operation refers to having an analog control channel, and either an analog voice/traffic channel or a digital voice/traffic channel (DTC). The AVC or DTC are used for actual communications, and the ACC is used to transfer information relating to, for example, call set-ups, service provider identification, and the other overhead or system information.
A newer standard, the EIA/TIA IS 136 standard supports communications covered by both analog and dual mode cellular, and also includes a totally digital communication scheme which was designed for the PCS frequency bands A-F and cellular frequency bands "a" and "b". This standard allows for a digital traffic channel (DTC) and a digital control channel (DCCH). In the case of the DTC, not only is the voice or data communicated, but in addition, a digital channel locator (DL) is transmitted in the DTC. The DL enables a mobile communication device that locks onto the DTC to use the information in the DL to locate a DCCH for purposes of obtaining information such as the SOC, SID, paging information, or other system overhead information carried on the digital control channel.
When a mobile communication device such as a mobile telephone attempts to register with the service provider, it locks onto a control channel and reads information such as the SOC and SID. If the SOC and/or SID correspond to a service provider with which the user has a communication services agreement, the telephone may register with the service provider's mobile communication system via the uplink control channel.
FIG. 2 illustrates different service-provider assignments in different parts of the United States. The Figure is a map of the United States illustrating assignments in cities such as Seattle, Chicago and Washington, DC. In Seattle, for example, frequency band A has been licensed to SOC (Service Operator Code) 001 with a SID of 43 and band C has been licensed to SOC 003 with a SID of 37. In Chicago, suppose that frequency band C has been licensed to SOC 001 with a SID of 57, and that band B has been licensed to SOC 003 with a SID of 51. In Washington, DC suppose that frequency band "a" has been licensed to a SOC 001 with a SID of 21, and that band A has been licensed to SOC 003 with a SID of 17. It should be noted that the same SOC may be found in several different locations although on different frequency bands. It should also be noted that the same SOC will be associated with different SIDs in each geographical area and that in the same geographic area different service providers have different SIDs. If a particular subscriber to a wireless telecommunication service has an agreement with a service provider having a SOC of 001, that subscriber would prefer to use systems with a SOC of 001 because the subscriber is likely to receive a less expensive rate. When the subscriber is in Seattle he/she would prefer to be on band A, and if in Chicago on band C, and if in Washington, DC on band "a".
The above described situation presents a problem for a wireless communication service subscriber. As a subscriber moves from one area of the country to another, the telephone, when turned on, searches for the "home" service provider, or a service provider with which the subscriber has a pre-arranged agreement. If, for example, the subscriber travels from Seattle to Chicago, then when the phone is turned on for the first time in Chicago, the phone will search through the different bands of the spectrum to identify the service operator with the code 001 in order to find the desired service provider.
In order to find a particular service provider, the phone may have to search through both the "a" and "b" cellular bands, and through the six PCS bands. It should be recalled that there are up to 21 different ACCs in each of the "a" and "b" cellular bands. It may be necessary to check 42 ACCs in order to find an ACC from which a SOC or SID may be obtained. Additionally, searching for a particular SOC or SID in PCS bands A through F is particularly time consuming, because, within a particular PCS band, the digital control channels (DCCHs), which contain the SOC and SID, are not assigned to specific frequencies. As a result, the mobile communication device may find it necessary to search through the spectrum of each PCS band looking for a DCCH, or an active DTC that has a digital channel locator (DL) which will direct the mobile communication device to the DCCH. Accordingly, the process of searching for a particular service provider is laborious and may require a period of time on the order of several minutes.
In the related applications cited above there are disclosed intelligent roaming techniques in which a particular search schedule is used to optimize the search for a preferred service provider. In some of the disclosed intelligent roaming techniques, the improved roaming search "schedule may be reprogrammed using signals received over the wireless communication channel" or based on "the prior history of the mobile communication device's use." Additionally, as disclosed in U.S. patent application Ser. No. 08/597,066 filed Feb. 5, 1996 entitled "Roaming Authorization System", a subscriber defined profile may be stored at the Home Location Register. Roaming authorization is then only granted consistent with permitted roaming time-windows in that profile.